A variety of alloys for living tissues are used in surgeries and implants in the medical field.
For example, Ti—Ni alloys have advantages such as high strength, wear resistance, corrosion resistance, and high compatibility with living tissues, etc., and are used as materials for living tissues in various medical appliances.
However, Ti—Ni light alloys have poor processability and their cold processing rate is limited, usually within a range of 30%˜40%; therefore, additional processing procedures such as intermediate annealing are required. Consequently, these alloys require high processing cost, and their application in products with complex shapes is limited. Moreover, in Ti—Ni alloy materials for living tissues, the Ni element may cause allergy symptoms. Therefore, researches have been made to develop materials for living tissues that are more safer without using the elements that may cause toxic or allergic risks to living tissues.
With respect to such materials for living tissues, the techniques described in the following patent documents 1˜4 are known.
In FIG. 3 of patent document 1 (Japanese Patent Document JP3521253), a Ti—Nb—Sn shape memory alloy for living tissues, composed of niobium within a range of 10 at %˜20 at %, tin within a range of 3 at %˜8 at %, and titanium that accounts for the remaining portion (74 at %˜86 at %), is disclosed. In the technique disclosed in patent document 1, as illustrated by the stress-strain curve shown in FIG. 10, the maximum recoverable strain (maximum strain—residual strain after unloading) has an elasticity of 3.5% only.
In patent document 2 (Japanese Patent Document JP3884316), a Ti—Mo—Ga super-elastic titanium alloy for living tissues, composed of molybdenum (Mo) within a range of 2 at %˜12 at %, gallium (Ga) less than 14 at %, and titanium (Ti) that accounts for the remaining portion, and a Ti—Mo—Ge super-elastic titanium alloy for living tissues, composed of molybdenum within a range of 2 at %˜12 at %, germanium (Ge) less than 8 at %, and titanium that accounts for the remaining portion, are disclosed.
In patent document 3 (Japanese Patent Document JP4128975), a Ti—Nb—(Au, Pt, Pd, Ag) super-elastic titanium alloy for living tissues is disclosed, and the composition of the alloy is as follows: the amount of niobium is within a range of 5 mol %˜40 mol %, the amounts of Au, Pt, Pd and Ag are lower than 10 mol % respectively and the total amount of Au, Pt, Pd and Ag is lower than 20 mol %, and titanium accounts for the remaining portion.
In patent document 4 (Japanese Patent Document JP4302604), a Ti—(Ta, Nb)—Zr—Mo super-elastic titanium alloy for living tissues is disclosed, and the composition of the alloy is as follows: the amount of tantalum (Ta) is x mol %, the amount of niobium (Nb) is y mol %, and 15 mol≦1.5x+y≦45 mol %, the amount of zirconium (Zr) is within a range of 1 mol %˜20 mol %, the amount of molybdenum (Mo) is within a range of 1˜6 mol %, and the total amount of Ta, Nb, Zr, and Mo is lower than 60 mol %, and titanium account for the remaining portion. In addition, in patent document 4, as illustrated by the stress-strain curve shown in FIG. 2 and FIG. 3, the elasticity is up to 4%.